1. Field of the Invention
The invention relates to an image reading apparatus for reading an object image and outputting an image signal.
2. Related Background Art
Hitherto, as shown in a cross sectional view of FIG. 11, an image sensor which is in contact with an original to be read and reads an image is constructed by: an image sensor board 2 on which a sensor IC 1 is installed; a lens array 3 for guiding a reflected light from the original illuminated by an illuminating unit 4 to the sensor IC 1; a cover glass 5 which is come into contact with the original; and a frame 6 for positioning and holding those component elements.
As an illuminating unit 4, a unit as shown in a cross sectional view and a top view of FIG. 12 is used. The illuminating unit 4 is constructed by: LEDs 7 of a lead frame type serving as light sources provided on both ends; an optical guide member 8 arranged in a longitudinal direction for converting a light irradiated from the LEDs into a line-shaped light; and a housing 9 having a square cross sectional shape for positioning and holding the LEDs 7 and optical guide member 8. An electric power is supplied to the LED 7 from a power source (not shown) through a lead 11.
When such an illuminating unit 4 is attached to the frame, as shown in FIG. 11, in order to illuminate the light from the oblique direction of 45xc2x0 for the original, an attaching surface which is inclined by 45xc2x0 for the original mounting surface is provided for the frame 6, and the surface corresponding to one side of a square in the cross section of the housing 9 constructing the illuminating unit 4 is come into contact with the inclined attaching surface and is adhered by both-side adhesive tape or the like, thereby positioning and fixing.
However, in the conventional image sensor mentioned above, since the housing of the illuminating unit having the square cross section is installed to the frame so as to be inclined by 45xc2x0 for the original surface, there are the following problems.
(1) To enclose the illuminating unit into the frame, it is necessary that a length of diagonal line in the cross section of the housing of the illuminating unit is assured in the vertical direction in the frame. However, the image sensor main body cannot be largely formed. Therefore, a thickness of frame with which the lower portion of the illuminating unit is come into contact has to be made thin. It is difficult to work the frame. Even if the frame can be worked, a mechanical strength of the frame is insufficient.
(2) An angle at which the illuminating unit is attached to the frame is not equal to 45xc2x0 depending on an individual difference of each image sensor and an optical axis is deviated, so that there is a case where an illuminance on the original reading line doesn""t reach a specified value.
(3) To fix the illuminating unit to the frame, not only a material such as both-side adhesive tape or adhesive agent is necessary but also a step of attaching such a material is added, so that manufacturing costs rise.
It is an object of the invention to enable an image to be read at a high quality.
Another object of the invention is to provide an image reading apparatus of a high mechanical strength.
Still another object of the invention is to miniaturize an image reading apparatus.
Further another object of the invention is to suppress a variation in reading lines due to a deviation of an optical axis.
To accomplish the above objects, according to an embodiment of the invention, there is provided an image reading apparatus comprising: illuminating means for illuminating an object in a line shape; image forming optical system for forming a light, as an image, from an object illuminated by the illuminating means; a line sensor for converting the light formed as an image by the image forming optical system into an image signal; and holding means for holding the illuminating means and the line sensor, wherein a shape formed by connecting vertices in at least a part of a cross section of the illuminating means by straight lines is set to a polygon of a pentagon or more.
According to another embodiment, there is provided an image reading apparatus comprising: illuminating means which is constructed by a point light source and optical guide means for guiding and converting a light from the point light source into a line-shaped light and illuminate an object in a line shape; an image forming optical system for forming the light, as an image, from the object illuminated by the illuminating means; a line sensor for converting the light formed as an image by the image forming optical system into an image signal; and holding means for holding the illuminating means and the line sensor, wherein at least a part of a cross section of the illuminating means has a circular shape.
According to still another embodiment, there is provided an image reading apparatus comprising: illuminating means for illuminating an object in a line shape; an image forming optical system for forming the light, as an image, from the object illuminated by the illuminating means; a line sensor for converting the light formed as a n image by the image forming optical system into an image signal; and holding means for holding the illuminating means and the line sensor, wherein at least a part of the cross sectional shape of the illuminating means has a circular shape and a convex portion is formed on the outer periphery of the circular shape and is come into engagement with a concave portion formed in the holding means, thereby certainly positioning.
According to further another embodiment, there is provided an image reading apparatus comprising: illuminating means for illuminating an object in a line shape; an image forming optical system for forming a light, as an image, from an object illuminated by the illuminating means; a line sensor for converting the light formed as an image by the image forming optical system into an image signal; and holding means for holding the illuminating means and the line sensor, wherein at least a part of the cross sectional shape of the illuminating means has a circular shape and a concave portion is formed on the outer periphery of the circular shape and is come into engagement with a convex portion formed in the holding means, thereby certainly positioning.
With the above construction, a cross sectional area of the illuminating means is small and an enough mechanical strength can be assured while miniaturizing the apparatus. Further, by certainly positioning the illuminating means, a variation in reading line can be suppressed and an image can be read at a high quality.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.